从一个片段传递到另一个片段

Question

    FragmentManager fragmentManager = getSupportFragmentManager();
    fragmentManager.beginTransaction().replace(R.id.flContent, fragment).commit();// this line has the problem

这是我完整的logcat：

FATAL EXCEPTION: main                                                                               java.lang.NullPointerException                                        

在Android.support.v4.app.backStackRecord.doaddop（backStackRecord.java:414)在Android.support.v4.app.backStackRecord.replace（backStackRecord.java:449)在Android.support.v4.app.backStackRecord.replace（backStackRecord.java:441)在Android.support.v4.app.backStackRecord.replace（backStackRecord.java:441)在Android.support.v4.app.backStackRecord.replace（id.support.v7.view.menu.menuBuilder.dispatchMenuItemSelect(MenuBuilder.java:811)在Android.support.v7.view.menu.menuItemimpl.invoke(MenuItemimpl.java:152)在Android.support.v7.view.menu.menuBuilder.performItemAction(MenuBuilder.java:152)在Android.support.v7.view.menu.menuBuilder.navigationMenuPresenter HandleCallback（handler.java:725)在Android.os.handler.DispatchMessage（handler.java：92）在Android.os.looper.loop（looper.java：176）在Android.app.activitythread.main（activitythread.java：5319）在java.lang.reflect.Method.invokenative（原生方法）在java.lang.reflect.Method.invoke（Method.java：511）在.System.NativeStart.Main（本机方法）

MainActivity.java

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        txResult = (TextView) findViewById(R.id.txResult);
        toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        mDrawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        nvDrawer = (NavigationView) findViewById (R.id.nvView);
        setupDrawerContent(nvDrawer);}



    private void setupDrawerContent(NavigationView navigationView) {
        navigationView.setNavigationItemSelectedListener(
                new NavigationView.OnNavigationItemSelectedListener() {
                    @Override
                    public boolean onNavigationItemSelected(MenuItem menuItem) {
                        selectDrawerItem(menuItem);
                        return true;
                    }
                });
    }

    public void selectDrawerItem(MenuItem menuItem) {
        // Create a new fragment and specify the planet to show based on
        // position
        Fragment fragment = null;

        Class fragmentClass;
        switch(menuItem.getItemId()) {
            case R.id.nav_first_fragment:
                fragmentClass = MainActivity.class;
                break;
            case R.id.nav_second_fragment:
                fragmentClass = SecondActivity.class;
                break;
            case R.id.nav_third_fragment:
                fragmentClass = ThirdActivity.class;
                break;
            default:
                fragmentClass = MainActivity.class;
        }

        try {
            fragment = (Fragment) fragmentClass.newInstance();
        } catch (Exception e) {
            e.printStackTrace();
        }

        // Insert the fragment by replacing any existing fragment
        FragmentManager fragmentManager = getSupportFragmentManager();
        fragmentManager.beginTransaction().replace(R.id.flContent, fragment).commit();

        // Highlight the selected item, update the title, and close the drawer
        menuItem.setChecked(true);
        setTitle(menuItem.getTitle());
        mDrawer.closeDrawers();
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // The action bar home/up action should open or close the drawer.
        switch (item.getItemId()) {
            case android.R.id.home:
                mDrawer.openDrawer(GravityCompat.START);
                return true;
        }

        return super.onOptionsItemSelected(item);
    }

   // @Override
   // protected void onPostCreate(Bundle savedInstanceState) {
   //     super.onPostCreate(savedInstanceState);
   // 

secondactivity.java

 private void setupDrawerContent(NavigationView navigationView) {
        navigationView.setNavigationItemSelectedListener(
                new NavigationView.OnNavigationItemSelectedListener() {
                    @Override
                    public boolean onNavigationItemSelected(MenuItem menuItem) {
                        selectDrawerItem(menuItem);
                        return true;
                    }
                });
    }

    public void selectDrawerItem(MenuItem menuItem) {
        // Create a new fragment and specify the planet to show based on
        // position
        Fragment fragment = null;

        Class fragmentClass;
        switch(menuItem.getItemId()) {
            case R.id.nav_first_fragment:
                fragmentClass = MainActivity.class;
                break;
            case R.id.nav_second_fragment:
                fragmentClass = SecondActivity.class;
                break;
            case R.id.nav_third_fragment:
                fragmentClass = ThirdActivity.class;
                break;
            default:
                fragmentClass = SecondActivity.class;
        }

        try {
            fragment = (Fragment) fragmentClass.newInstance();
        } catch (Exception e) {
            e.printStackTrace();
        }

        // Insert the fragment by replacing any existing fragment
        FragmentManager fragmentManager = getSupportFragmentManager();
        fragmentManager.beginTransaction().replace(R.id.flContent, fragment).commit();

        // Highlight the selected item, update the title, and close the drawer
        menuItem.setChecked(true);
        setTitle(menuItem.getTitle());
        mDrawer.closeDrawers();
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // The action bar home/up action should open or close the drawer.
        switch (item.getItemId()) {
            case android.R.id.home:
                mDrawer.openDrawer(GravityCompat.START);
                return true;
        }

        return super.onOptionsItemSelected(item);
    }

    // @Override
    // protected void onPostCreate(Bundle savedInstanceState) {
    //     super.onPostCreate(savedInstanceState);
    // }

Answer 1

您的问题不清楚，因为您没有发布完整的类代码，以及您得到的是什么错误。

我所理解的是，当导航抽屉中的一个项目被选中时，您希望更改片段。类似于Gmail应用程序，当用户从收件箱文件夹移动到发送文件夹或任何其他文件夹时。

如果您正在尝试这样做，您需要创建一个活动，插入一个片段。当选择导航抽屉中的一个项目时，应根据导航抽屉中选择的选项将当前片段替换为新片段。